Coal liquefaction by hydrogenation



Patented Mar. 15, 1949 COAL LIQUEFACTION BY HYDROGENATION Henry H.Storch and Lester L. Hirst, Pittsburgh, Pa., assignors to the UnitedStates of America as represented by the Secretary of the Interior NoDrawing. Application December 24, 1943, Serial No. 515,474

1 Claim.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. 757) The invention described herein may be manufactured and usedby or for the Government of the United States for governmental purposeswithout the payment to us of any royalty thereon in accordance with theprovisions of the act of April 30, 1928 (Ch. 460, 45 Stat. L. 467) This.invention relates to hydrogenation, and more particularly to thedestructive hydrogenation of solid carbonaceous materials susceptiblethereto. Still more particularly, this invention relates to a lowpressure process for the production of liquid hydrocarbons from coals,such as bituminous coal, lignite and the like, as well as to novelcatalysts for carrying out the process.

Heretofore solid carbonaceous materials susceptible to destructivehydrogenation have been reacted with hydrogen at extremely highpressures ranging from 500 to 1,000 atmospheres to produce liquidhydrocarbons which have been employed for fuel oils and the like.However, the employment of extremely high pressure requires specializedand expensive equipment. Certain low pressure processes are also knownfor the production of liquid hydrocarbons from solid carbonaceousmaterials, such processes in general comprising the treatment of thesolid carbonaceous materials with highly-hydrogenated solvents such astetra-hydro-naphthalene, deca-hydronaphthalene, hydrogenated cresol, andthe like. The principal difliculty with such solvent extractionprocesses resides in the fact that large quantities of gummy or tarryresidues result, which rapidly render the equipment useless.

It is therefore an object of the present invention to provide a lowpressure process for the destructive hydrogenation of solid carbonaceousmaterials susceptible thereto. Another object is to provide a processfor the preparation of liquid hydrocarbons from normally solidcarbonaceous materials. A further object is to provide a process for thedestructive hydrogenation of solid carbonaceous materials susceptiblethereto in which the re-precipitation and repolymeriaztion of said solidcarbonaceous materials is prevented. Yet a further object is to providea continuous process for the preparation of fuel oil from coal which canbe carried out for extended operating periods. Another object is toprovide novel and eflective catalysts for carrying out the foregoingprocesses.

The foregoing and other objects hereinafter apparent are accomplished inaccordance with the present invention wherein a solid carbonaceousmaterial susceptible to destructive hydrogenation is admixed with aliquid vehicle and a' dispersed catalyst, the mixture is heated to atemperature of at least 300 0., introduced together with excess hydrogeninto a closed reaction zone maintained under an elevated pressure of notmore than 90 atmospheres, then said mixture is advanced through thereaction zone while the.temperature of the reaction mixture isprogressively elevated as the mixture is advanced, and the reactionmixture is discharged from the reaction zone at a final temperature ofnot more than 475 C. It has been discovered that repolymerization andre-precipitation of the normally solid carbonaceous material beingdestructively hydrogenated can be prevented by maintaining a controlledprogressively increasing reaction temperature as the destructivehydrogenation is carried out. By beginning the destructive hydrogenationat a relatively low temperature, and progressively increasing thetemperature in the reaction mixture as the reaction progresses, thedeposition of coke and other residues in the equipment is substantiallycompletely inhibited. The initial temperature of reaction is at least300 C., and preferably within the more restricted range of from 350 C.to 400 C. Thereafter the temperature within the reaction zone isprogressively elevated, as the reaction proceeds, to a maximumtemperature of not more than 475 C. Preferably, the final reactiontemperature is maintained within the more restricted range of from 425C. to 450 0.

Suitable solid carbonaceous materials susceptible to destructivehydrogenation in accordance with the present invention include lignite,brown coal, subbituminous or bituminous coals, and preferablysubbituminous coals such as the Monarch Bed coal of Wyoming and thelike.

In preparing the coal or other carbonaceous material susceptible todestructive hydrogenation for reaction in accordance with the presentinvention, it is desirable to pulverize to a relatively fine state ofsub-division, preferably such that it will pass through a standard Tylerscreen of about mesh. After being pulverized, the coal is admixed with asufficient amount of one of the usual liquid vehicles for destructivehydrogenation, preferably a recycle oil produced by a previoushydrogenation. In general, from one to three parts by weight of recycleoil or other liquid vehicle per part of coal provides a suitably fluentconsistency for reaction. In starting a new plant, a topped hightemperature coal tar which has been hydrogenated as hereinafter to beexplained, provides a desirable liquid vehicle. It is preferable toavoid liquid vehicles derived from petroleum or other aliphatic sources.

' This invention also provides novel catalysts for carryingout the lowpressure destructive hydrogenation of carbonaceous materials susceptiblethereto, the cataiystsbeing a, dispersed catalyst comprising astanniferous substance in intimate admixture with a halogenoussubstance, and as a fixed or contact catalyst, a stainless steel. Boththe dispersed catalyst and the stainless steel catalyst are extremelyeffective whenemployed separately, but when employed together, they areremarkably effective at low pressures and low temperatures in inhibitingthe precipitation of coke-like materials.

Suitable stanniferous substances include metallic tin, and tin compoundssuch as tin sulfide, oxide, oxalate, or other tin compound soluble instrong mineral acids. In general, about 0.05 per- 'cent to 0.5 percentby weight and preferably between 0.1 percent and 0.3 percent by weightof the stanniferous substance "based on moistureand ash-free solidcarbonaceous material is a sufflcient amount. The halogenous substanceemployed in the dispersed catalyst can be molecular chlorine, bromine,or iodine, and the like, but it is preferably in the form of an alkylhalide, or other volatile halogen compound. Iodoform con stitutes apreferred halogenous substance and in general, iodine or iodinecompounds are superior to other halogenous substances. Usually from 0.02percent to 0.2 percent by weight, based on moistureand ash-free coal orother solid carbonaceous material susceptible to destructivehydrogenation, is a sufficiently large amount of iodoform or otherhalogeneous catalytic substance. Greater or lesser amounts of theforegoing components of the dispersed catalyst can be employed, Thedispersed catalyst is admixed with the dispersion of solid carbonaceousmaterial in the liquid vehicle; and in the hydrogenation of coal,between 0.004 part and 0.006 part by weight of a mixture of equal partsby weight of tin sulfide and iodoform per part by weight of coal hasbeen found to give a desired rate of hydrogenation.

While the foregoing dispersed catalyst alone will catalyzehydrogenation, it has been found that a still more beneficial effectupon the reaction can be secured when the reaction mixture, during atleast the latter stages of the reaction, is passed over a fixed catalystcomprising a stain less steel. Suitable stainless steels includeaustenitic steel alloys with chromium and nickel which may also containcobalt, molybdenum and the like, such as KAzSMO, Rezistall, andpreferably the stainless steel which contains about 18 percent by weightof chromium and 8 percent nickel, the balance being largely iron. Thestainless steel fixed catalyst is preferably in the form of wire,ribbons, machine turnings, or other form presenting a large surface tothe reactants. The entire re-actlon vessel can be packed with thestainless steel catalyst, but it has been found, in. general, thatpacking the latter half of the reaction zone with stainless steelcatalyst provides a suitable catalytic effect. By-the latter half of thereaction zone is meant that portion which is maintainedat the higherstages of reaction temperature, for example, above 400 C.

By the employment of the foregoing progressively increasing temperatureschedule and catsired reaction, a suitable hydrogen pressure within thereaction zone being not more than 90 atmospheres, generally from 30 to80 atmospheres,

and preferably the pressure is maintained withinthe more restrictedrange of 50 to '75 atmospheres.

In carrying out the destructive hydrogenation of coal or othercarbonaceous materials susceptible thereto, the dispersed catalyst isadded to the previously prepared coal-oil paste and then preheated tothe initial reaction temperature.

alyst, it has been found that a relatively low Thereafter the mixture isintroduced into a suitable reaction vessel together with a large excessof hydrogen and the reactioncommences smoothly. The reaction isexothermic in character and ingeneral, a progressively increasingtemperature gradient is secured by suitable heating and cooling meansforming a part of the converter system. As the material is passedthrough the convertersystem, the desired temperature gradient ismaintained by heating and cooling, and the material is subjected toreaction for a contact time of between one-half and eight hours. andpreferably for only about one to three hours, a reaction time of twohours being an average value. The reaction vessel in theportionnextadjacent the exit thereof is preferably packed with stainless steelturnings, and the reaction mixture containing dispersed catalyst thusultimately contacts this fixed catalyst. After the reaction iscompleted, the reaction mixture is cooled, the pressure letdown toatmospheric, gaseous by-products and excess hydrogen discharged and thefinal mixture subjected to a topping distillation. Material boilingbelow 235 C. is separated from the remaining oily product, catalystsludge and ash. The lower boiling material, which contains the tar acidsand bases, is then successively washed with an aqueous acid materialsuch as sulfuric acid andthereafter with aqueous alkali such as causticsoda solution, to remove said tar acids and bases. Approximately 2percent of the reaction material comprises these industrially valuabletar acids and bases. The material boiling above 235 C. is subjected tocentrifugal'separation, the ash being thereby reduced to 0.01 to 0.03percent by weight of the final oil. The centrifuge product and thewashed product are then mixed together and meet the specifications ofthe American Society for Testing Materials for number 5 and number 6fuel oil. The heating value of the product is higher than the heatingvalue of similar oils produced from petroleum.

A more specific procedure is to pass through a converter a mixture ofone part of powdered coal with one to two parts of a heavy recycle oil,and between 0.004 and 0.006 part of a mixture of equal parts by weightof tin sulfide and iodide in a hydrogen atmosphere under a pressure of60 to 70 atmospheres and a temperature maintained at from 370 to 385 C.at entry and 400 to 415 C. at the point of exit of the reacting mixture,passing the reacting mixture through a second converter packed withbright stainless steel turnings under an initial temperature of from 410to 420 C. and under a temperature of from 430 to 440 C. at the point ofexit, sub- ,iecting the product of the second converter to a fractionalcondensation and removing solid particles of the fluid product bycentrifuging.

The following examples illustrate how the invention may be carried out,but it is not limited thereto. Parts are by weight unless otherwisedesignated:

Example 1 One part bituminous coal from the Black Creek Bed in WalkerCounty, Alabama, is pulverized to minus 80-mesh, (standard Tylerscreen), and admixed with two parts of liquid vehicle, 0.001 part tinsulfide and 0.0005 part iodoform. (The liquid vehicle is prepared byhydrogenation of topped coke-oven tar at from 415 to 435 C. under apressure of 65 to 70 atmospheres for 3 hours, in the presence of 0.001part tin sulfide and 0.0005 part iodoform.) The mixture of coal, liquidvehicle, and dispersed catalyst is passed through a tubular preheater'made of stainless steel. The preheater is provided with heating andcooling means, and the temperature of the coal-oil paste is elevatedtherein to 120 C. A second preheater, similarly provided with heatingand cooling means, is arranged in series with the first one, wherein thecoal-oil paste is further preheated to 370 C. Thereafter, gaseoushydrogen, separately preheated also to 370 C., is admixed with thecoal-oil paste containing dispersed catalyst, and the gas-paste-catalystmixture is introduced into an elongated stainless steel converterprovided with suitable heating and cooling means, and having a length tointernal diameter ratio of to 1. An excess of hydrogen is preterablyemployed, the rate of hydrogen input being maintained between 5 andcubic feet per pound of coal-oil paste although only 0.063 part hydrogenper part coal is consumed. The pressure within the converter ismaintained at 65-70 atmospheres by suitable valves and pumps, and thereaction temperature within the converter is gradually elevated byheating to 390 C. Over 3 /2 hours reaction time, the temperature isgradually elevated to 415 C., after which the pressure is released, theproduct cooled, and an additional 0.001 part tin sulfide and 0.0005 partiodoform is added. A successive hydrogenation of the primary product iscarried out in a similar converter under similar conditions, but theinitial conversion temperature is adjusted to 415 C., the finaltemperature to 435 C., and the reaction time is 3 hours. The reactionmixture is cooled, the pressure let down to atmospheric and the reactionmixture centrifuged to remove ash and a small amount of residue. Theyield of oil produced, based on the weight of coal consumed, is 53.4percent. Eighty percent of the oil produced is recycled to serve asliquid vehicle for another batch, and 20 percent is a final product.After extended operating periods, no coke is found in the equipment. Theoil produced has the following characteristics:

Specific gravity at 26 C. 1.118 B. t. u. per pound 16,892 B. t. u. pergallon 157,600

Ash content, per cent 0.02, Viscosity, furol, seconds at 122 F 44.6Flash point, F. 225 Distillation (Topping, American Wood PreserversAssociation Method) volume percent to 350 C 35. Insoluble (Bureau ofMines Tetralin- Cresol Method) percent 5.7

About 1 to 2.5 volume percent of the oil boils below 235 C., and the oilcontains about 1 to 2' percent oxygen, in the form of tar acids,removable by washing with aqueous alkali solution.

Example 2 One part of Pittsburgh Bedbituminous coal is admixed with twoparts recycle oil (product of a previous run), and with, based onmoistureand ash-free coal, 0.3 percent tin sulfide and 0.15 percentiodoform. The coal-oil paste containing dispersed catalyst ishydrogenated in the apparatus of Example 1, with the exception that thelatter half of the converter, (the portion at the more elevatedtemperature), is packed with stainless steel turnings, containing 18percent by weight chromium and 8 per cent by weight nickel, the balancebeing principally iron. The coal-oildispersed catalyst mixture is passedcontinuously through the converter, the entrance temperature beingmaintained at 370 to 385 C., and the hydrogen pressure at 65-70atmospheres. During a reaction time of 1.5 hours, hydrogen consumptionis only 3 to 6 percent by weight based on moistureand ash-free coalconsumed, although a substantial excess of hydrogen is passed throughthe converter. No coke forms in the equipment, and the reacted materialis entirely soluble except for its ash content. The product of thehydrogenation is subjected to a topping distillation to remove materialsboiling below 235 C., and the residual material is centrifuged to removeash, catalyst residues, and a small amount of unreacted coal. Thefraction boiling below 235 C. is washed with dilute caustic soda anddilute sulfuric acid to remove industrially valuable tar acids andbases. The resulting neutral oil, when mixed'with the centrifuged oil,fills the specification of the American Society for Testing Materialsfor number 5 and number 6 fuel oil, while its heating value is higherthan similar oils produced from petroleum.

Although the fixed stainless steel catalyst is in general employedtogether with the dispersed catalyst, it nevertheless possesses decidedcatalytic properties apart from the dispersed catalyst and therefore canbe employed alone in the present invention. Likewise, the entireconverter can be packed with stainless steel turnings or other formthereof presenting extended surfaces.

The hydrogen employed for the hydrogenation process is preferablypurified so as to reduce the content of inert gas to less than 5percent. Small amounts of impurities such as sulfur compounds, carbonmonoxide, water vapor, and the like exert no apparent detrimental effectupon the reaction. The novel catalysts of the present invention areactive in the presence of sulfur compounds and therefore appreciableamounts of sulfur compounds can be tolerated.

It will be apparent that the foregoing invention provides a novel methodfor the preparation of liquid hydrocarbons from coal or other normallysolid carbonaceous materials susceptible to destructive hydrogenation,and that a relatively low pressure is required in comparison withprevious processes. By the employment of the temperature ranges and thetemperature gradient of the present invention, the deposition of cokeand other undesired materials in the reaction apparatus is substantiallycompletely inhibited, thus permitting operation for extended periods offrom 500 to 1,000 hours or more without any attention being required.The coal employed is converted to oil in good yield, while there-precipitation or re-polymerization of coal is inhibited by thepresent invention. v

Since many apparently widely differing embodiments of the presentinvention will occur to one skilled in the art, it is apparent thatvarious changes may be made in the invention without departing from thespirit and scope thereof.

What is claimed is:

A process of producing fuel oil directly from coal which comprisesputting into a converter a mixture of one part of powdered coal with oneto two parts of a heavy recycle oil, and between 0.004 and 0.006 part ofa mixture of equal parts by weight of tin sulfide and iodide in ahydrogen atmosphere under a pressure of 60 to "70 atmospheres and atemperature maintained at from 370 C. to 385 C. at entry and from 400 C.to 415 C. at the point of exit of the reacting mixture passing thereacting mixture through a sectional condensation and removing solidparticles REFERENCES CITED The following references are of record in thefile of this patent:

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Peters Aug. 22, 1944

